1. Field of the Invention
The present invention relates to a method of clamping a pair of rails in the proper relative positional relation when pressure welding the rails at their end faces and a clamping apparatus for performing the method.
2. Description of the Prior Art
The joining conditions of a joint obtained by pressure welding a pair of rails at their end faces or the joint conditions such as the occurrence of any lateral displacement or variation in the level of the upper surface of the joint and the straightness of the joint have great effects on the riding confortability in a trolley, running stability, the magnitude of noize, etc., and particularly greater accuracy is required for the joints of rails on which the trolley is run at high speeds. Such defects of the rail joint are due to the manufacturing accuracy of the rails themselves or the clamping accuracy of the rails before their pressure welding and therefore the rails to be joined must be properly placed end to end in the correct relative positional relation by absorbing the manufacturing accuracy of the rails, particurly variations in the bend of the rails during clamping of the rails prior to their welding.
On example of this type of method and apparatus for clamping a pair of rails during their pressure welding is disclosed, for example, in Japanese Laid-Open Patent Application No. 56-136292 assigned to the assignee of the present application. However, since this conventional clamping method employs a system of simultaneously effecting the vertical and lateral clamping a pair of rails by a single hydraulic cylinder unit through link means, during the clamping operation the hydraulic cylinder unit must be operated after both of vertical position adjustments and lateral position adjustments of the rails with respect to each other have been completed and particularly the lateral position adjusting operation required that the operator crawls under the pressure welding machine to replace the pair of clamping jaws bolted to clamping means or insert adjusting spacers for lateral position adjusting purposes. Since this operation is repeated several times along with an operation of confirming the straightness of the pair of rails, since usually as long as about 10 minutes are required for properly clamping the rails in a straight line and since the following pressure welding itself is completed in only a few minutes, there is a disadvantage that almost all the time for the whole operation must be spent for the position adjusting operation of the rails.